U.S. patent number 6,848,180 [Application Number 10/470,696] was granted by the patent office on 2005-02-01 for turbocharger turbine shaft joining method.
This patent grant is currently assigned to Shimizu Turbo Technology. Invention is credited to Masami Shimizu.
United States Patent |
6,848,180 |
Shimizu |
February 1, 2005 |
Turbocharger turbine shaft joining method
Abstract
A joining method providing improved joining accuracy for wheel
and turbine shaft. A part of the inner peripheral wall of a fitting
hole of a wheel is tapered inwardly from the opening of the fitting
hole. At one end of the turbine shaft to be joined to the wheel, a
tapered axial abutment portion is provided. In the turbine shaft,
an axial abutment portion is provided in a part other than the
portion to be fused by welding to suppress deformation at the time
of fusion. The axial abutment portion is tapered, and the inner
peripheral wall of the fitting hole is tapered, whereby the wheel
and the turbine shaft are brought into close contact with each
other while positioned coaxially. As such, close contact is
effected in a stable manner in the axial abutment portion where
tapered surfaces come into contact with each other.
Inventors: |
Shimizu; Masami (Chiba,
JP) |
Assignee: |
Shimizu Turbo Technology
(Chiba, JP)
|
Family
ID: |
18898048 |
Appl.
No.: |
10/470,696 |
Filed: |
July 30, 2003 |
PCT
Filed: |
February 08, 2002 |
PCT No.: |
PCT/JP02/01091 |
371(c)(1),(2),(4) Date: |
July 30, 2003 |
PCT
Pub. No.: |
WO02/06495 |
PCT
Pub. Date: |
August 22, 2002 |
Foreign Application Priority Data
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Feb 9, 2001 [JP] |
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2001-034439 |
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Current U.S.
Class: |
29/889.2;
416/213R; 416/244R |
Current CPC
Class: |
F01D
5/025 (20130101); F02B 39/00 (20130101); F05D
2220/40 (20130101); Y10T 29/4932 (20150115); F05D
2230/64 (20130101); F05D 2250/232 (20130101); F05D
2230/233 (20130101) |
Current International
Class: |
F01D
5/02 (20060101); F02B 39/00 (20060101); F01D
005/02 () |
Field of
Search: |
;416/213R,244R
;29/889.2 |
References Cited
[Referenced By]
U.S. Patent Documents
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4983064 |
January 1991 |
Kawaguchi et al. |
5084329 |
January 1992 |
Kato et al. |
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Foreign Patent Documents
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U 64-41633 |
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Mar 1989 |
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JP |
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A 2-173322 |
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Jul 1990 |
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JP |
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A 2001-254627 |
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Sep 2001 |
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JP |
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Primary Examiner: Nguyen; Ninh H.
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
What is claimed is:
1. A turbocharger turbine shaft joining method for joining together
a wheel and a turbine shaft, the method comprising: obtaining a
wheel having a fitting hole into which one end portion of a turbine
shaft is to be inserted for fixation, wherein at least a part of an
inner peripheral wall of the fitting hole of the wheel is tapered
so as to be reduced in diameter inwardly from the opening of the
fitting hole; positioning the turbine shaft in a rotation axis of
the wheel, wherein at the one end of the turbine shaft to be joined
to the wheel are a tapered axial abutment portion capable of being
brought into close contact with the tapered inner peripheral wall
and an insertion portion with a fixed diameter to be inserted into
the fitting hole; and joining and fixing the wheel and the turbine
shaft to each other so as to be coaxial in the rotation axis.
2. A turbocharger turbine shaft joining method according to claim
1, characterized in that the turbine shaft is provided with an
abutment portion abutting against a surface provided in the fitting
hole and restricting axial movement of the turbine shaft at the
time of welding.
3. A turbocharger turbine shaft joining method according to claim
2, characterized in that: an insertion portion with a fixed
diameter is formed at one end of the turbine shaft; and an axial
abutment portion connected to the insertion portion and tapered so
as to gradually increase in diameter from the insertion portion is
provided, both the insertion portion and the axial abutment portion
being coaxially arranged.
4. A turbocharger turbine shaft joining method according to claim
2, characterized in that the wheel and the turbine shaft are welded
to each other by fusing a part other than the axial abutment
portion of the turbine shaft and the tapered inner peripheral wall
of the wheel.
5. A turbine wheel for use in a joining method according to claim
2, characterized in that at least a part of the inner peripheral
wall of the fitting hole into which one end portion of the turbine
shaft is to be inserted is tapered so as to reduce in diameter
inwardly from the opening of the fitting hole.
6. A turbine shaft for use in a joining method according claim 2,
characterized in that provided at one end of the turbine shaft to
be joined to the turbine wheel are a tapered axial abutment portion
capable of being brought into close contact with the tapered inner
peripheral wall of the fitting hole formed in the turbine wheel and
an insertion portion with a fixed diameter to be inserted into the
fitting hole.
7. A turbocharger turbine shaft joining method according to claim
1, characterized in that: an insertion portion with a fixed
diameter is formed at one end of the turbine shaft; and an axial
abutment portion connected to the insertion portion and tapered so
as to gradually increase in diameter from the insertion portion is
provided, both the insertion portion and the axial abutment portion
being coaxially arranged.
8. A turbine wheel for use in a joining method according claim 7,
characterized in that at least a part of the inner peripheral wall
of the fitting hole into which one end portion of the turbine shaft
is to be inserted is tapered so as to reduce in diameter inwardly
from the opening of the fitting hole.
9. A turbine shaft for use in a joining method according claim 7,
characterized in that provided at one end of the turbine shaft to
be joined to the turbine wheel are a tapered axial abutment portion
capable of being brought into close contact with the tapered inner
peripheral wall of the fitting hole formed in the turbine wheel and
an insertion portion with a fixed diameter to be inserted into the
fitting hole.
10. A turbocharger turbine shaft joining method according to claim
1, characterized in that the wheel and the turbine shaft are welded
to each other by fusing a part other than the axial abutment
portion of the turbine shaft and the tapered inner peripheral wall
of the wheel.
11. A turbine wheel for use in a joining method according to claim
1, characterized in that at least a part of the inner peripheral
wall of the fitting hole into which one end portion of the turbine
shaft is to be inserted is tapered so as to reduce in diameter
inwardly from the opening of the fitting hole.
12. A turbine shaft for use in a joining method according to claim
1, characterized in that provided at one end of the turbine shaft
to be joined to the turbine wheel are a tapered axial abutment
portion capable of being brought into close contact with the
tapered inner peripheral wall of the fitting hole formed in the
turbine wheel and an insertion portion with a fixed diameter to be
inserted into the fitting hole.
13. A turbine shaft according to claim 12, characterized in that:
an insertion portion with a fixed diameter is formed at one end of
the turbine shaft; and a tapered portion connected to the insertion
portion and gradually increasing in diameter is provided, the
insertion portion and the tapered portion being arranged
coaxially.
14. A turbocharger turbine shaft joining method for joining
together a wheel and a turbine shaft, the method comprising:
obtaining a wheel having a fitting hole into which one end portion
of a turbine shaft is to be inserted for fixation; positioning a
turbine shaft in a rotation axis of the wheel; and inserting an
insertion portion with a fixed diameter at one end of the turbine
shaft to be joined to the wheel into the fitting hole, wherein on
the insertion portion is an abutment portion abutting against a
surface formed in the fitting hole and restricting axial movement
of the turbine shaft to thereby prevent axial movement of the
turbine shaft at the time of welding.
Description
TECHNICAL FIELD
The present invention relates to a method of joining wheels
(turbine wheel and compressor wheel) and a turbine shaft used in a
supercharger (turbocharger) of an internal combustion engine.
BACKGROUND ART
Regarding an internal combustion engine mounted in an automobile or
the like, a technique is known according to which a turbocharger
for compressing intake air is provided in order to achieve an
improvement in charging efficiency to thereby improve the engine
output. Generally speaking, such a turbocharger is driven by
utilizing the energy of exhaust gas discharged from the internal
combustion engine.
In a turbocharger, a turbine housing provided at some midpoint in
an exhaust passage and a compressor housing provided at some
midpoint in an intake passage are connected to each other through
the intermediation of a center housing, and a turbine wheel
rotatably supported in the turbine housing and a compressor wheel
rotatably supported in the compressor housing are coaxially
connected through the intermediation of a turbine shaft rotatably
supported in the center housing.
In such a turbocharger, exhaust gas discharged from the internal
combustion engine flows into the turbine housing through an exhaust
inlet, and this exhaust gas flows along a scroll passage in an
eddy-like fashion. Then, it flows from the scroll passage to a
nozzle passage before it is blown against the turbine wheel to
thereby rotate the turbine wheel.
When the turbine wheel is thus rotated, the torque of the turbine
wheel is transmitted to the compressor wheel through the turbine
shaft, and the compressor wheel rotates in synchronism with the
turbine wheel. When the compressor wheel rotates in synchronism
with the turbine wheel, the intake air in the vicinity of the
intake air inlet is sucked in the compressor housing by a sucking
force generated by the rotation of the compressor wheel and sent
under pressure to an intake air outlet by way of a send-out passage
and the scroll passage.
Thus, the intake air compressed in the compressor housing is
forcibly supplied to the combustion chamber, so that the charging
efficiency of the intake air is improved. In this process, the fuel
injection amount is increased in response to the increase in the
intake air amount, whereby it is possible to obtain larger
combustion power and explosive power, making it possible to enhance
the engine output.
At this time, the turbine wheel must rotate at a high speed of from
100,000 to 160,000/min. while being exposed to exhaust with a
maximum temperature as high as 900.degree. C. Thus, in the
production of a turbocharger, the turbine wheel, the compressor
wheel, and the turbine shaft must be arranged with high accuracy in
the same rotation axis. In particular, it is very important that no
production error (deviation in rotation axis of the wheel and the
turbine shaft) should be generated when joining them together.
Conventionally, the wheel and the turbine shaft are often joined by
electron beam welding; in this case, the product accuracy depends
on the accuracy with which the pre-welding processing (edge
preparation) is performed.
Conventionally, this edge preparation has been performed as
follows.
First, as shown in FIG. 9, a fitting hole 51 is formed in a turbine
wheel 50, and a protrusion 61 is formed at one end of one turbine
shaft 60 on the side joined to the turbine wheel 50. This
protrusion 61 is fitted into the fitting hole 51 so as to generate
a gap portion 52, and one end of the turbine shaft 60 is abutted
against the turbine wheel 50 at an abutment portion 53 to perform
positioning.
In another method, the turbine wheel and the turbine shaft are
abutted against each other, and positioning is performed in a
condition in which they are secured by a welding jig.
Of those conventional methods, the former method requires provision
of a clearance at the fitting portion 52 taking into account the
deformation at the time of welding, etc., so that, due to the play,
it is rather difficult to secure the coaxiality of the turbine
wheel 50 and the turbine shaft 60.
Further, at the time of joining, the entire periphery of the
abutment portion 53 is fused by electron beam welding or the like,
and the fusion of the abutment portion 53 is likely to lead to
bending deformation at this portion.
Further, since the turbine shaft 60 is contracted in the axial
direction, a problem occurs such as the dimensional accuracy in the
axial direction is likely to be lost.
In the latter method, the positioning of the turbine wheel 50 and
the turbine shaft 60 depends upon the accuracy of the jig used, so
that it is rather difficult to secure stable coaxiality. Further,
due to the variation in the jig and secular change, it is difficult
to maintain accurate coaxiality.
In addition, as in the former method, the entire abutment portion
of the turbine wheel and the turbine shaft is fused by electron
beam welding or the like so that bending deformation is likely to
occur at this portion. Further, since the turbine shaft contracts
in the axial direction, a problem occurs such as the dimensional
accuracy in the axial direction is likely to be lost.
In particular, in the above conventional methods, a part of the
turbine shaft (abutment portion 53) is fused by welding, so that
the turbine shaft 60 contracts. In view of this, the turbine wheel
50 and the turbine shaft 60 are first welded, and, thereafter, as
shown in FIG. 10, adjustment of the bending of the shaft main body
of the turbine shaft 60 and minute processing of the thrust
bearing, etc. provided at one end thereof must be executed for
improvement in general accuracy. Specifically, after welding the
structure with a contour as indicated by the solid line in FIG. 10,
this turbine shaft 60 has to be cut into the shape as indicated by
the two-dot chain line, executing adjustment of the axis and minute
processing of the thrust bearing, etc. Thus, as compared with the
case in which processing is performed solely on the turbine shaft
60 before welding, the processing is hard to perform and requires a
lot of time.
The present invention has been made in view of the above problems.
It is a technical object of the present invention to provide a
joining method which makes it possible to achieve an improvement in
the joining accuracy for the wheel and the turbine shaft.
DISCLOSURE OF THE INVENTION
In order to achieve the above-mentioned object, according to the
present invention, the following measures are employed.
That is, in a turbocharger turbine shaft joining method for joining
together a wheel having a fitting hole into which one end portion
of a turbine shaft is to be inserted for fixation and a turbine
shaft to be positioned concentrically to a rotation axis of the
wheel, the method is characterized in that at least a part of an
inner peripheral wall of the fitting hole of the wheel is tapered
so as to be reduced in diameter inwardly from the opening of the
fitting hole, that provided at one end of the turbine shaft to be
joined to the wheel are a tapered axial abutment portion capable of
being brought into close contact with the tapered inner peripheral
wall and an insertion portion with a fixed diameter to be inserted
into the fitting hole, and that the wheel and the turbine shaft are
joined and fixed to each other so as to be coaxial in the rotation
axis.
In the method, it is possible to be constructed such that an
insertion portion with a fixed diameter is formed at one end of the
turbine shaft, and a tapered portion is provided, which is
connected to the insertion portion and gradually increased in
diameter from the insertion portion, whereby the insertion portion
and a larger diameter portion being coaxially arranged.
In this case, the wheels include a turbine wheel, compressor wheel,
etc. which are coaxially connected together through the
intermediation of a turbine shaft which is rotatably supported.
Also, it is possible to be constructed such that the wheel and the
turbine shaft are welded to each other by fusing a part other than
the axial abutment portion of the turbine shaft and the tapered
inner peripheral wall of the wheel.
It is preferable for the turbine wheel used in the above method
that at least a part of the inner peripheral wall of the fitting
hole into which one end portion of the turbine shaft is to be
inserted is tapered so as to reduce in diameter inwardly from the
opening of the fitting hole.
Here, the turbine shaft adapts such a structure that provided at
one end of the turbine shaft are a tapered axial abutment portion
capable of being brought into close contact with the tapered inner
peripheral wall of the fitting hole formed in the turbine wheel and
an insertion portion with a fixed diameter to be inserted into the
fitting hole. In this case, it is possible to have such a structure
that an insertion portion with a fixed diameter is formed at one
end of the turbine shaft, and that a tapered portion connected to
the insertion portion and gradually increasing in diameter is
provided, whereby the insertion portion and the tapered portion
being arranged coaxially.
It is possible to apply the turbocharger of the present invention
to the production of all manner of turbochargers, such as variable
turbo, combustible nozzle turbo, linear chassis turbo, and
sequential turbo, as long as it is of the type having wheels and a
turbine shaft.
In the present invention, it is possible to be constructed such
that an axial abutment portion is provided in a part other than the
portion of the turbine shaft fused by welding, so that it is
possible to prevent change in axial dimension when the turbine
shaft undergoes fusion contraction.
Further, it is possible to be constructed such that the axial
abutment portion is formed in a tapered configuration, and on the
other hand, at least a part of the inner peripheral wall of the
fitting wall coming into contact therewith is also formed in a
tapered configuration, whereby the wheel and the turbine shaft are
brought into close contact with each other without fail, and they
are guided so as to be positioned coaxially, thereby making it
possible to easily secure accuracy in coaxiality.
Further, it is possible to be constructed such that, in addition to
the axial abutment portion, there is provided an insertion portion
having a fixed diameter, thereby stabilizing the close contact
property of the axial abutment portion where tapered surfaces come
into contact with each other.
At the same time, due to the tapered axial abutment portion, the
movement in the direction perpendicular to the axial direction of
the turbine shaft is restricted, so that it is possible to prevent
the turbine shaft from being bent by the heat at the time of
welding.
It is possible to be constructed such that, in addition to the
axial abutment portion, the turbine shaft can have, at a position
other than the portion fused by welding, an abutment portion which
abuts a surface formed in the fitting hole and which restricts
axial movement of the turbine shaft at the time of welding, whereby
displacement of the turbine shaft is reliably prevented.
In the method, it is possible to be constructed such that an
insertion portion with a fixed diameter to be inserted into the
fixing hole is provided at one end of the turbine shaft to be
joined to the wheel instead of providing the tapered axial abutment
portion, and that provided on the insertion portion is an abutment
portion abutting against a surface formed in the fitting hole and
restricting axial movement of the turbine shaft, so that it is
possible to prevent axial movement of the turbine shaft at the time
of welding.
In the present invention, when joining together the wheel and the
turbine shaft by a means such as welding, it is possible to prevent
change in dimension due to axial contraction of the turbine shaft
4, thereby making it possible to achieve an improvement in product
accuracy.
In particular, when joining together the wheel equipped with a
fitting hole into which one end portion of the turbine shaft is to
be inserted for fixation and the turbine shaft to be positioned in
the rotation axis of this wheel, it is possible to be constructed
such that at least a part of the inner peripheral wall of the
fitting hole of the wheel is tapered inwardly from the opening of
the fitting hole, and on the other hand, at one end of the turbine
shaft to be joined to the wheel, there are provided a tapered axial
abutment portion capable of coming into close contact with the
inner peripheral wall and an insertion portion to be inserted into
the fitting hole and having a fixed diameter, whereby the wheel and
the turbine shaft can be easily arranged coaxially, thereby
simplifying the processing step and achieving an improvement in
product accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a sectional view of a turbine wheel according to the
present invention;
FIG. 2 is a side view of a turbine shaft according to the present
invention;
FIG. 3 is a diagram showing a state in which the turbine wheel and
the turbine shaft are joined together;
FIG. 4 is an enlarged view of portion A of FIG. 3, showing the
joint portion of the turbine wheel and the turbine shaft;
FIG. 5 is a diagram showing the joint portion of the turbine wheel
and the turbine shaft according to another embodiment;
FIG. 6 is a diagram showing the joint portion of the turbine wheel
and the turbine shaft according to still another embodiment;
FIG. 7 is a perspective view, partially broken away, showing the
construction of a turbocharger;
FIG. 8 is a flowchart showing a process for joining together a
turbine wheel and a turbine shaft;
FIG. 9 is a diagram showing a conventional example in which a
turbine wheel and a turbine shaft are joined together; and
FIG. 10 is a diagram showing how a conventional turbine shaft is
processed.
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the turbocharger turbine shaft joining method of the
present invention will now be described with reference to the
drawings.
Embodiment 1
As shown in FIG. 7, in a turbocharger 12, a compressor housing 13
and a turbine housing 14 are connected to each other through the
intermediation of a center housing 15; in the center housing 15, a
turbine shaft 4 is supported so as to be rotatable around its axis
L. One end portion of the turbine shaft 4 protrudes into the
compressor housing, and a turbine wheel 1 equipped with a plurality
of blades 2 is mounted to the protruding portion.
In the following, the method of joining together the turbine shaft
4 and the turbine wheel 1, used in the turbocharger 12 constructed
as described above, will be described in detail.
(Edge Preparation for Turbine Wheel)
The turbine wheel 1, which is rotated by the force of exhaust flow,
has blades 2 formed around a cylindrical main body. As shown in
FIG. 1, in the rotation axis L, there is provided a cylindrical
fitting hole 3 into which the turbine shaft 4 is inserted for
fixation. An inner peripheral wall 3a of the fitting hole 3 is
equipped with a step portion 3b, and the entire periphery of the
inner peripheral wall extending from the step portion 3b toward the
opening of the fitting hole 3 constitutes a large diameter portion
3c whose diameter is larger than that of the forward end portion of
the fitting hole 3. The entire periphery of the inner peripheral
wall of the portion nearer the opening than the large diameter
portion 3c is tapered so as to increase in diameter toward the
opening, and this portion constitutes a tapered edge portion
3d.
An edge preparation as described above is performed on the turbine
wheel 1 for connection with the turbine shaft 4 by welding.
As shown in FIG. 2, the turbine shaft 4 is a cylindrical shaft, at
one end of which there is provided a head portion 5 to be inserted
into the fitting hole 3 for fixation. The head portion 5 has a
larger diameter than the middle portion of the turbine shaft 4 and
has a thrust bearing 5a, etc.
The forward end portion of the head portion 5 is equipped with an
insertion portion 6 with a fixed diameter, i.e., without any change
in diameter, and the insertion portion 6 is connected to a tapered
axial abutment portion 7 with a gradually increasing diameter, the
insertion portion 6 and the axial abutment portion 7 being arranged
substantially coaxially.
After being endowed with an approximately proper contour, this
turbine shaft 4 undergoes heat treatment for increased hardness,
and finish processing through polishing.
(Joining of Turbine Wheel and Turbine Shaft)
Next, a process for joining together the turbine wheel 1 and the
turbine shaft 4, processed as described above, will be
described.
After cleaning the turbine wheel 1 and the turbine shaft 4, the
head portion 5 of the turbine shaft 4 is inserted into the fitting
hole 3 of the turbine wheel 1. At this time, as shown in FIGS. 3
and 4, the insertion portion 6 is fitted into the fitting hole 3 to
realize a so-called faucet engagement; the forward end 6a, however,
does not abut the bottom 8 of the fitting hole 3, leaving a small
gap 10 between the forward end of the insertion portion 6 and the
bottom 8 of the fitting hole 3. The gap 10 is provided for the
purpose of reducing, if to a small degree, the heat transmission
from the turbine wheel 1 to the turbine shaft 4 during operation of
the turbocharger.
The tapered abutment portion 7 of the turbine shaft 4 abuts the
tapered edge portion 3d in the inner periphery of the fitting hole
3; since the tapered portions are brought into close contact with
each other, positioning of the turbine shaft 4 in the direction of
the axis L is effected automatically, the two components being
guided coaxially. Thus, the turbine wheel 1 and the turbine shaft 4
are brought into close contact with each other in a stable manner
without involving any play.
In addition, the insertion portion 6 reaches the innermost small
diameter portion of the fitting hole 3, and the peripheral side
surface of the insertion portion 6 and the inner peripheral wall 3a
with small diameter are brought into contact with each other, so
that the axial abutment portion 7 and the tapered edge portion 3d
are brought into close contact with each other in a very stable
manner.
The positional relationship between the insertion portion 6 and the
axial abutment portion 7 is not restricted to that of this
embodiment. For example, it is also possible to provide a tapered
portion in the innermost portion of the fitting hole 3 and use this
portion as the axial abutment portion, with the insertion portion
for stabilizing the close contact being situated on the opening
side of the fitting hole 3. By positioning the tapered axial
abutment portion 7 as near to the opening of the fitting hole 3 as
possible, the joint error in the axial direction can be easily
reduced, thereby achieving an improvement in the joining accuracy
of the turbine wheel 1 and the turbine shaft 4.
(Welding)
As shown in FIGS. 3 and 4, when the insertion portion 6 of the
turbine shaft 4 is inserted into the fitting hole 3 of the turbine
wheel 1 to bring the axial abutment portion 7 into close contact
with the tapered edge portion 3d, the tapered peripheral edge
portion 3d of the fitting hole 3 of the turbine wheel 1 and the
protrusion 5 provided next to the axial abutment portion 7 of the
turbine 4 are opposed to each other, with a small gap being
generated therebetween. The tapered peripheral edge portion 3d and
the protrusion 5 are joined together by electron beam welding.
Since the melting point of the turbine shaft 4 is lower than that
of the material of the turbine wheel 1, the protrusion 5 is melted
earlier than the peripheral edge portion 3d of the opening. FIG. 4
shows a fused welding portion 11. This welding is performed on the
entire periphery of the tapered peripheral edge portion 3d and the
protrusion 5, and the turbine wheel 1 and the turbine shaft 4 are
integrally joined together. As shown in the drawing, the fused
portion 11 is at a position separate from the axial abutment
portion 7. Due to this fusion, the turbine shaft 4 is prevented
from becoming shorter, thus preventing change in the axial length
of the shaft. The accuracy in the axial direction of the turbine
shaft 4 is maintained by the axial abutment portion 7.
The generation of bending stress due to heat in the turbine shaft 4
as a result of the welding performed on the entire periphery of the
tapered peripheral edge portion 3d and the protrusion 5 can be
coped with through control in a direction perpendicular to the
rotation axis direction by the axial abutment portion 7, so that it
is possible to prevent the turbine shaft 4 from being bent by
welding.
In the following, the process for joining together the turbine
wheel 1 and the turbine shaft 4 will be illustrated with reference
to the flowchart of FIG. 8.
In step 1, edge preparation is performed on the turbine wheel 1.
Here, the fitting hole 3 into which the axial abutment portion 7 is
fitted is provided, and a plurality of blades 2 are formed in the
outer periphery, thus substantially completing the turbine
wheel.
In step 2, the turbine shaft 4 is prepared by forming a steel
material into a shaft, regulating the configuration of the shaft
and the head portion, imparting hardness to the whole through
induction hardening, and performing finish polishing thereon.
Next, in step 3, the turbine wheel 1 and the turbine shaft 4 are
cleaned.
After the cleaning, in step 4, the turbine wheel 1 and the turbine
shaft 4 are joined to each other by electron beam welding.
In step 5, finish processing is performed on the shroud portion of
the turbine wheel 1.
Next, in step 6, the balance of the whole is adjusted, and, in step
7, cleaning is performed thereon for completion.
As described above, in accordance with this embodiment, the axial
abutment portion 7 is provided in a part other than the portion
fused by welding, so that it is possible to prevent axial
dimensional change in the turbine shaft 4.
Further, solely by bringing the axial abutment portion 7 and the
tapered peripheral edge portion 3d into close contact with each
other, in other words, solely by inserting the insertion portion 6
into the fitting hole 3 to abut the turbine wheel and the turbine
shaft 4 against each other, the turbine wheel 1 and the turbine
shaft 4 are guided so as to be arranged coaxially, whereby accuracy
in coaxiality can be easily secured.
Further, by providing the insertion portion 6 having a fixed
diameter along with the axial abutment portion 7, the axial
abutment portion 7 and the tapered peripheral edge portion 3d are
held in close contact with each other in a very stable manner,
whereby the turbine shaft 4 is little subject to axial
deviation.
At the same time, due to the axial abutment portion 7, movement of
the turbine shaft 4 is also restricted in a direction perpendicular
to the axial direction, so that it is possible to effectively
prevent bending of the turbine shaft 4 due to the heat at the time
of welding.
Further, the step of polishing the turbine shaft after joining it
to the turbine wheel 1 for the regulation of its shape, is
eliminated, whereby it is possible to reduce the processing work
and difficulty involved.
While in the embodiment described above the turbine shaft and the
turbine wheel are joined together, it goes without saying that the
same technique is applicable to the connection of the turbine shaft
with the compressor wheel. Further, there is no particular
limitation regarding the means for the connection; it is possible
to adopt a welding process other than electron beam welding or some
other connecting means.
Embodiment 2
While in Embodiment 1 the gap 10 exists between the insertion
portion 6 and the bottom 8 of the fitting hole 3, it is also
possible to adopt a construction in which there is provided an
abutment portion 38 as shown in FIG. 5.
In the embodiment shown in FIG. 5, a step portion 31 is formed on
an inner peripheral wall 30 of the fitting hole 3, and this step
portion 31 has a surface 32 perpendicular to the rotation axis of
the turbine shaft 4. The forward end portion beyond the step
portion 31 (the left-hand portion in the drawing) is formed as a
small diameter portion 33.
The turbine shaft 4 has at its forward end a protrusion 34 to be
inserted into the small diameter portion 33, and a step portion 36
is formed between the protrusion 34 and the outer peripheral
portion 35 of the turbine shaft 4. The corner of the step portion
36 is beveled into a flat portion 37.
In this way, there is formed an abutment portion 38 where the step
portion 31 of the fitting hole 3 and the step portion 36 of the
turbine shaft 4 abut against each other when joining the turbine
wheel 1 and the turbine shaft 4 to each other. When joining the two
components, thus constructed, to each other by welding, a portion
other than the abutment portion 38, in this case a welding portion
39 situated behind the abutment portion 38 (on the right-hand side
in FIG. 5), is fused. Therefore, the abutment portion 38 is not
fused, which, in synergy with the tapered axial abutment portion 7,
more reliably helps to prevent change in dimension due to the axial
contraction of the turbine shaft 4.
Embodiment 3
As shown in FIG. 6, in this embodiment, in the connection between
the turbine shaft 4 and the turbine wheel 1, the insertion portion
6 is inserted into the fitting hole 3 without providing a tapered
axial abutment portion. A step portion 31 is formed on the inner
peripheral wall 30 of the fitting hole 3, and the step portion 31
has a surface 32 perpendicular to the turbine shaft 4. The forward
end portion beyond the step portion 31 (on the left-hand side in
the drawing) is formed as the small diameter portion 33.
The turbine shaft 4 has at its forward end a protrusion 34 to be
inserted into the small diameter portion 33, and a step portion 36
is formed between the protrusion 34 and the outer peripheral
portion 35 of the turbine shaft 4. The corner of the step portion
36 is beveled into a flat portion 37.
In this way, there is formed an abutment portion 38 where the step
portion 31 of the fitting hole 3 and the step portion 36 of the
turbine shaft 4 abut against each other when joining the turbine
wheel 1 and the turbine shaft 4 to each other. When joining them to
each other by welding, a part other than the abutment portion 38,
in this case a welding portion 39, is fused, whereby it is possible
to prevent change in dimension due to axial contraction of the
turbine shaft 4.
In this case, to coaxially arrange the turbine wheel 1 and the
turbine shaft 4, a gap S between the inner peripheral wall 30 of
the fitting hole 3 and the outer peripheral wall 35 of the turbine
shaft 4 is made as small as possible, and the turbine shaft 4 is
forced into the fitting hole 3, whereby it is possible to arrange
them coaxially, with practically no error involved.
INDUSTRIAL APPLICABILITY
The present invention is applicable to the manufacturing of a
turbocharger device for an internal combustion engine, making it
possible to provide a high quality turbocharger device with an
improved joining accuracy for the turbine wheel and the turbine
shaft.
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